Some people have problems with getting images the original size as they get thumbnails all the time. Some people do not. The sequence you see below works for me but I know it does not work for others.
This is a 3meg .swf file which will show me getting an image, uploading the image and publishing it. It gets published at full size.
If you do NOT see this when doing the above, can you post here and explain what you do see?